Power grinder with safety guard and spindle arresting means

ABSTRACT

A portable power grinder has a housing, a rotating output shaft with a grinding wheel mounting device, a grinding wheel safety guard adjustable between angular positions defined by apertures in the safety guard, and a manually operable safety guard arresting device engageable with an aperture. The arresting device has a lock slide movable on the housing and operable by an articulated lever connected at one end to the housing and at another end to the lock slide and being shifted by folding and unfolding, thereby moving the lock slide between a safety guard arresting position and a safety guard releasing position and locking the lock slide in the arresting position. The lock slide includes a spring exerting a force onto the safety guard in the arrested position. A lock spindle displaceably supported on the lock slide moves between a retracted safety guard locking position and an advanced position to lock the output shaft.

The invention relates to a power grinder having a motor driven outputshaft with a grinding tool mounting device, and a grinding tool safetyguard adjustably supported on the tool housing between a number ofpre-selected angular positions defined by apertures in the safety guard,and a manually operable arresting device for locking the safety guard inanyone of the pre-selected positions by engaging either one of theapertures.

A power grinder of the above mentioned type is previously described inU.S. Pat. No. 5,766,062.

A problem concerned with power grinders of the above type is thegeneration of vibrations and an annoying noise due to rattling of thesafety guard during operation of the grinder. In order to guarantee thatthere will always be a light fit between the safety guard and thehousing to facilitate adjustment of the safety guard, there will alwaysbe a play between the safety guard and the housing, and often this playwill be rather big due to a normal spreading of manufacturing toleranceson the parts involved. This means that in many cases there will be roomfor vibrational movements of the safety guard which causes not only arattling noise but also undesired vibrations in the grinder housing.

The main object of the invention is to provide a power grinder with aneasily adjustable safety guard, and a safety guard arresting devicehaving a means for avoiding the above mentioned problem.

Another object of the invention is to provide a power grinder having anadjustable safety guard and a safety guard arresting device, wherein thesafety guard arresting device is provided with a manually operable meansfor temporarily locking the output shaft of the grinder at change ofgrinding tool.

Further characteristics and advantages of the invention will appear fromthe following specification and claims.

A preferred embodiment of the invention is below described in detailwith reference to the accompanying drawings.

IN THE DRAWINGS

FIG. 1 shows a bottom view of a power grinder according to the inventionand illustrates the arresting device in its safety guard releasingposition.

FIG. 2 shows a side view of the power grinder in FIG. 1.

FIG. 3 shows a bottom view of the power grinder in FIG. 1 andillustrates the arresting device in a safety guard arresting position.

FIG. 4 shows a side view of the power grinder in FIG. 3.

FIG. 5 shows a bottom view of the power grinder in FIG. 1 andillustrates the arresting device in a safety guard arresting position aswell as in an output shaft locking position.

FIG. 6 shows a side view of the power grinder in FIG. 5.

FIG. 7 shows a perspective view of the arresting device according to theinvention.

The power grinder shown in the drawing figures comprises a housing 10including a motor (not shown), a rear handle 11, a side handle 12, andan angle head 13 supporting a rotating output shaft 14. The output shaft14 is provided with a mounting device 15 for a grinding wheel.

At the forward end of the housing 10 there is supported a grinding wheelsafety guard 18 which is arranged to partly surround the grinding wheelto protect the operator and other people and equipment in the vicinityof the grinder should the grinding wheel break up and desintegrate athigh speed. The safety guard 18 has an inner circular flange 17 foradjustably supporting the safety guard 18 on the angle head 13, and anouter part-circular flange 19. The outer flange 19 is provided with arow of apertures 21 for arresting the safety guard 18 in a number ofpre-selected angular positions as described in further detail below.Also the inner flange 17 has a number of apertures 20 for lettingthrough a lock spindle as described below.

On its underside, the tool housing 10 is formed with a dovetail shapedguide channel 22 extending in the longitudinal direction of the housing10 and being directed towards the output shaft 14. In this guide channel22 there is movably guided a lock slide 24 for movement towards and awayfrom, respectively, the output shaft 14. For guiding of the lock slide24 in the dovetail shaped channel 22 the lock slide 24 itself is formedwith a congruent dovetail shaped guide portion 23. Moreover, the lockslide 24 is provided with a contact portion 25 with a crest formedcontact surface 26 for abutting engagement with the outer flange 19 ofthe safety guard 18. Two studs 27,28 are secured to the contact portion25 for engagement with two at a time of the apertures 21 in the outerflange 19 as the lock slide 24 occupies its safety guard 18 arrestingposition. See FIG. 1.

The lock slide 24 is operated by an articulated lever 30 which comprisestwo halves 31, 32 one of which, the rear half 31, is pivotally connectedto the housing 10 via a pivot pin 33 and connected to the other forwardhalf 32 via a joint pin 34. The forward lever half 32 is pivotallyconnected to the lock slide 24 via a pivot pin 35. The rear lever half31 comprises a wave shaped leaf spring element, and when the lever 30 isshifted from a folded position, as illustrated in FIG. 2, to an unfoldedposition, as illustrated in FIGS. 4 and 6, the leaf spring element 31 iscompressed longitudinally to thereby exert a pre-tensioning force on thelock slide 24. In such unfolding movement the lever 30 is forced toperform an over-centre movement, which means that the centre of thejoint pin 34 moves past a straight centre line A-A extending through thecentres of the pivot pins 33 and 35. See FIG. 4. The pre-tension forceexerted by the compression of the spring element 31 urges the centrepart of the lever 30 and the joint pin 34 against the housing 10 tothereby maintain the lock slide 24 in the safety guard abuttingposition. A weak torsion spring 36 is arranged around the pivot pin 33to exert a bias force on the lever half 31 towards the folded positionof the lever 30 as illustrated in FIG. 2 with the purpose to maintainthe lock slide 24 in a release position and facilitate adjustment of thesafety guard 18.

In order to facilitate manuevering of the lever 30, the forward leverhalf 32 has a rear extension 37 which is formed as a tangent to bepressed by the operator at shifting of the lever 30 toward the unfoldedposition.

On the lock slide 24 there is displaceably supported a lock spindle 38which is longitudinally shiftable between a first retracted position inwhich it engages the apertures 21 in the outer safety guard flange 19,when the lock slide 24 occupies its active safety guard 18 arrestingposition (see FIG. 3) and a second extended position in which it alsoengages one of a number of indentations 39 in the output shaft 14 forlocking the latter against rotation. A spring 38 a is arranged to biasthe lock spindle 38 towards the retracted position as illustrated inFIGS. 1, 2 and 3.

At its rear end, the lock spindle 38 is provided with a maneuver head 40by which the lock spindle 38 is manually shiftable between its firstretracted position as in FIGS. 1, 2 and 3 and its second extendedposition as in FIGS. 5 and 6. In the same way as the lock slide 24, themaneuver head 40 is formed with a dovetail shaped guide portion 42 forsliding engagement with the channel 22 in the housing 10. The head 41 isformed with a rear transverse shoulder 43, and the lever half 32 hashook like edges 44 for co-operation with the shoulder 43 as the lever 30occupies its unfolded position and the lock spindle 38 occupies itsretracted position. By this co-operation the lever 30 is locked againstaccidental shifting towards its folded safety guard 18 releasingposition.

A support member 46 is secured to the housing 10 adjacent the outputshaft 14 and is provided with a non-illustrated through opening forguidingly receiving the forward end of the lock spindle 38 in thearresting position of the lock slide 24. The support member 46 isintended to transfer side forces to which the lock spindle 38 issubjected primarily at the output shaft 14 locking position asillustrated in FIGS. 5 and 6.

The different operating positions of the safety guard arresting deviceare illustrated in the drawing figures to which is referred inconnection with the following description. As an example, it is assumedthat the arresting device occupies its safety guard releasing positionas illustrated in FIGS. 1 and 2. In this position the articulated lever30 occupies its folded position, and the lock slide 24 is withdrawn fromits co-operation with the safety guard flange 19, i.e. the contactportion 25 as well as the studs 27, 28 are disengaged from the flange19, and the lock spindle 38 is withdrawn from the apertures 21 in theflange 19. The lever 30 is maintained in this folded position by thetorsion spring 36.

When the safety guard 18 has been put in a desired angular positionrelative to the angle head 13, the lever 30 is shifted by means of thetangent 37 from its folded position (see FIGS. 1 and 2) to its unfoldedposition (see FIGS. 3 and 4), thereby shifting the lock slide 24together with the lock spindle 38 into arresting engagement with theouter flange 19 and the apertures 21. In this arresting position, thecontact portion 25 abuts via its contact surface 26 against the flange19, and the studs 27,28 engage two of the apertures 21 in the flange 19.The lock spindle 38 penetrates through the apertures 21 in the flange 19and extends via the apertures 20 in the inner flange 17 into the supportmember 46. In this position of the arresting device not only a positivelocking engagement is obtained by the lock slide 24 and the lock spindle38 visavi the flange apertures 21, but a radial tension force is appliedon the flange 19 to prevent the safety guard 18 from rattling andvibrating during operation of the grinder.

The lever 30 is positively locked in its unfolded position by a latchingco-operation between the hook like edges 44 on the forward lever half 32and the shoulder 43 on the maneuver head 40. This locking action ismaintained as long as the lock spindle 38 and the maneuver head 40remain in their retracted positions.

As the centre of the joint pin 34 passes the straight line A-A throughthe centres of the pivot pins 33 and 35 the leaf spring element formingthe rear lever half 31 is longitudinally compressed, and when havingpassed the over-centre point the leaf spring element 31 is able toexpand to some extent but exerts a longitudinal tension force on thelever 30 such that the centre part with the joint pin 34 is forcedagainst the housing 10, against the action of the rather weak torsionspring 36. By this over-centre movement, the lever 30 forms an endwisesupport of the lock slide 24, and due to the action of the springelement 31 there is maintained an abutment force between the contactportion 25 and the flange 19. The grinder is now ready for operation.

When the grinding wheel attached to the output shaft 14 has to beexchanged for another one, the motor is stopped and the lock spindle 38is displaced forwards by means of the maneuver head 40 such that theforward end of the lock spindle 38 engages one of the indentations 39 inthe output shaft 14. Thereby, the output shaft 14 is locked againstrotation and the grinding wheel mounting device could be loosened andre-tightened as the grinding wheel is exchanged. See FIGS. 5 and 6.

As the lock spindle 38 and the maneuver head 40 are now displacedforwards, the locking engagement between the hook like edges 44 on theforward lever half 32 and the shoulder 43 on the maneuver head 40 isbroken which means that the lever 30 may be shifted to its foldedrelease position for enabling adjustment of the safety guard position.See FIGS. 1 and 2.

1-5. (canceled)
 6. A portable power grinder comprising a housing, arotating output shaft with a grinding wheel mounting device, a grindingwheel safety guard supported on the housing and adjustable between anumber of pre-selected angular positions defined by a row of aperturesin the safety guard, and a manually operable arresting device forlocking the safety guard in any one of said pre-selected positions byengaging one of said apertures, wherein the arresting device comprises:a lock slide movably supported on the housing, an articulated leverhaving one end connected to said lock slide and an opposite endconnected to the housing and arranged to move by folding and unfolding,respectively, said lock slide between a safety guard releasing positionand a safety guard arresting position, said lever being arranged to beshifted between its unfolded position and its folded position via anover-center movement, and to positively arrest said lock slide in saidsafety guard arresting position by supporting in its unfolded positionsaid lock slide relative to the housing, and a spring arranged to retainsaid lever firmly against the housing in said unfolded position.
 7. Apower grinder according to claim 6, wherein said lock slide comprises: alock spindle protruding in the movement direction of said lock slide forselectively engaging any one of said apertures in the safety guard, anda contact portion for abutting against a contact surface of the safetyguard, said spring being arranged to act substantially in thelongitudinal direction of said lever in said unfolded position state,thereby exerting a biasing force on said lock slide for obtaining acontact pressure between said contact portion and said contact surfaceof the safety guard and for maintaining said lock spindle in itsengagement with one of said apertures.
 8. A power grinder according toclaim 6, wherein: the output shaft is provided with at least oneindentation, and said lock spindle is displaceably guided on said lockslide for movement between a first position where it engages saidapertures in said safety guard only, and a second extended positionwhere it also engages said at least one indentation on said output shaftto thereby lock said output shaft against rotation at change of grindingtool, a bias spring is arranged to bias said lock spindle toward saidfirst position, and said lock spindle is provided with a head for manualshifting of said lock spindle from said first position to said secondextended position.
 9. A power grinder according to claim 7, wherein: theoutput shaft is provided with at least one indentation, and said lockspindle is displaceably guided on said lock slide for movement between afirst position where it engages said apertures in said safety guardonly, and a second extended position where it also engages said at leastone indentation on said output shaft to thereby lock said output shaftagainst rotation at change of grinding tool, a bias spring is arrangedto bias said lock spindle toward said first position, and said lockspindle is provided with a head for manual shifting of said lock spindlefrom said first position to said second extended position.
 10. A powergrinder according to claim 6, wherein said spring comprises a leafspring forming half of said articulated lever.
 11. A power grinderaccording to claim 7, wherein said spring comprises a leaf springforming half of said articulated lever.
 12. A power grinder according toclaim 8, wherein said spring comprises a leaf spring forming half ofsaid articulated lever.
 13. A power grinder according to claim 9,wherein said spring comprises a leaf spring forming half of saidarticulated lever.
 14. A power grinder according to claims 7, whereinsaid contact portion comprises at least one stud element arranged toengage at least one of said apertures in the safety guard arrestingposition of said lock slide.
 15. A power grinder according to claims 9,wherein said contact portion comprises at least one stud elementarranged to engage at least one of said apertures in the safety guardarresting position of said lock slide.
 16. A power grinder according toclaim 15, wherein said spring comprises a leaf spring forming half ofsaid articulated lever.
 17. A power grinder according to claim 14,wherein said spring comprises a leaf spring forming half of saidarticulated lever.